At present, the absorbent core of baby diapers, incontinence products, and feminine hygiene products is covered on the wearer's side, i.e. on the side facing the body, with at least two layers. An absorption and distribution layer of nonwoven fabric or reticulated foam material is positioned between the cover nonwoven fabric, i.e. the perforated film, and the absorbent core; as the name already indicates, it rapidly absorbs the bodily fluid (urine, thin feces, or menses) and distributes it, as uniformly as possible, to the absorbent core that lies underneath and is usually made up of cellulose and superabsorber powder. In this way, the human skin is kept dry, with the result of preventing skin irritations, on the one hand, and on the other hand, leakage of the bodily fluid caused by an exit to the side is prevented. On the back, the absorbent hygiene product is sealed with a water-proof film or a nonwoven fabric/film laminate, to prevent the bodily fluid from passing through.
For the acquisition and distribution layer, nonwoven fabrics thermally bonded in a hot-air-flow dryer or bonded with polymer dispersions, made of crimped, relatively coarse-titer fibers are known. The fibers have titers of more than 3.3. dtex and are preferably made up of polyesters (polyethylene terephthalate) and/or polyolefins, where for the purpose of fiber bonding in flow-through ovens, bicomponent fibers with a side-by-side or a core/mantle structure are used, and one of the two fiber components melts at a clearly lower temperature than the other component. Such nonwoven fabrics demonstrate a relatively high volume with regard to their low weight, and in particularly, a great thickness, immediately after their production. However, it is known that this initial thickness is already clearly reduced when the goods are rolled up under the tensions usual in practice, and that the compression conditions in the package make a further contribution to reducing the thickness.
Therefore, an attempt was made to find solutions to achieve a thickness not solely by more or less statistically distributed crimped fibers and their bonding, but to bring such crimped fiber nonwoven fabrics into the third dimension, which is described as the Z direction, by way of undulation or other geometric alignment. It has been shown that in this way, greater compression resistance can be achieved than with so-called high-loft nonwoven fabrics, with the result of a clearly lower loss in thickness when passing through the production steps for a diaper, including packaging and storage.
A laminate made up of film and pleated fiber sheet layers is described in WO 92/01401 (U.S. Pat. No. 5,611,791). The laminate is made up of a polypropylene monofilament film and polypropylene fibers that are undulated or aligned in the Z direction in other geometrical structures. The polypropylene fibers are intimately bonded to the polypropylene monofilaments in the valleys of the waves.
The method for the production of such a monofilament nonwoven fabric laminate is described in WO 98/06290. The carded polypropylene staple fiber sheets pass through the nip between two hot, intermeshing positive and negative rollers, are brought into wave shape there, and after leaving the calander roller nip are kept in this shape by blowing on and drawing off hot air, until the waves are finally bonded to the polypropylene fibers of the film, at their raised areas, by being pressed against the polypropylene film between a smooth roller and a corrugated roller. A disadvantage of this method and the resulting undulated laminate is the fact that the wave height in the product is determined exclusively by the wave height of the intermeshing positive and negative calander rollers and that this height is subject to severe limitations.
It is true that such a laminate demonstrates the desired undulation, but it is unsuitable as an acquisition and distribution layer, because the film prevents the bodily fluid from being passed on to the absorbent core.